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PRIMARY PURPOSE: To prevent product flashing through enhanced cooling.
This flush plan is most commonly seen in boiler feed water service. It is essentially a closed loop system; virtually the same product is repeatedly circulated between the seal and the heat exchanger. This arrangement is a much more efficient cooling system than API PLAN 21 and the exchanger itself will have longer life since it will operate at cooler temperatures. A water jacket is also used to further reduce the seal chamber temperature. The piping and installation of this system is critical to its success.
Guidelines for API PLAN 23:
1) The heat exchanger should be located as close to the seal as possible with a maximum distance of 3 feet.
2) The bottom of the heat exchanger should be approximately 12 inches above the shaft centerline.
3) Avoid sharp elbows or bends in the tubing. Use as gentle a sweep in the turns and always have an upward slope from the seal to the exchanger to avoid vapor locking.
4) There must be sufficient shaft surface speed for the pumping ring to be effective.
5) If possible, use .500" to .750", stainless steel tubing from the exchanger supplying cooled fluid to the seal. Tubing from the seal back to the exchanger can be .375" for 2" shafts and smaller. Use .500" for shaft sizes above 2".
6) Always slope horizontal runs of tubing slightly upward (1 to 5 degrees) from the seal to the exchanger to prevent low spots in the line where air can be trapped and vapor lock the system preventing flow.
7) Any valves used in the closed loop should be of the free flowing type.
8) Whenever possible, locate the pumping ring in the gland where tangential port approaches can be utilized and clearances can be more clearly controlled.
POTENTIAL PROBLEMS:
1) Air should be vented from the tubing and seal chamber before starting the pump. If not, a vapor locked system can cause the seal to overheat and shorten life dramatically.
2) Products that become viscous when cooled will prevent the pumping ring from circulating the fluid. Lines can become plugged. The pumping ring (plan 23) does not have sufficient head capacity to drive the viscous plug from the cooler. For these viscous applications that may clog due to low temperature, plan 21 coming off first stage discharge has more impetus to drive the plug from the cooler on startup.
3) Know that the exchanger will eventually plug up. The best way to check for fouling is to compare the current product and cooling water temperatures into and out of the exchanger to those measured when the system was installed. Note that a change in the flow rate of the product or cooling water can also affect these temperatures.
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Quality certification: |
ISO 9001-2008
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Payment terms: |
L/C
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Currency type: |
INR
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